1. Field of Invention
The present invention relates to an optical film and, more particularly, to an optical film of a backlight module, a display device, and an electro-optical device with the backlight module.
2. Description of Related Art
With progress of electro-optical technologies and the coming of digital times to cause the business of liquid crystal display (LCD) is flourishing. The LCD having the advantages of high quality of the image, small volume, light weight, low drive voltage, and low power consumption, LCD is broadly applied in consumer communication products or electronic products, such as personal digital assistants (PDAs), mobile phones, camcorders, notebooks, desktop computers, automobile displays, and projection televisions, and replaces cathode ray tube (CRT) to become the mainstream of displays.
LCD utilizes characteristics of liquid crystal to perform displaying. Comparing to the conventional CRT, LCD has more flexibility in size and weight. Therefore, LCD is commonly applied in various kinds of personal systems, e.g. mobile phone, PDAs, displays of digital cameras, televisions and billboards.
Presently, there is a trend for LCD to become lighter and thinner, especially when applied in mobile applications, e.g. notebooks, PDAs, and mobile phones. Meanwhile, it is an imperative to cost down of material and fabrication. However, there is a conflict/trade-off in LCD panels between the downscaling of weight and size, and the robustness of the structure.
FIG. 1 is an explosion diagram of a backlight module of a conventional LCD panel. As illustrated in FIG. 1, for reducing the weight and the size, the backlight module 10 of the conventional LCD panel usually includes a plastic frame 102, a lower diffuser 104, prism films 106 and 108, and an upper diffuser 110. There is a reflector (now shown) and a light tube (now shown) disposed on the plastic frame 102, and a light guide plate (now shown) disposed between the plastic frame 102 and the lower diffuser 104. The fixed position of the optical films, e.g. the lower diffuser 104, the prism films 106 and 108, and the upper diffuser 110, after the fabricated within the plastic frame 102, are important. If optical films are loosely fixed on the plastic frame 102, the loosely fixed films avoid strain and torsion coming from the expansion of films when the temperature varies but causes displacement of the optical films such that the uniformity illustrated on the LCD is loss. However, the optical films tightly fixed on the plastic frame 102 solves the problem of the displacement of the optical films but results in uneven expansion of the films when the temperature varies whatever also destroys the uniformity of the LCD. For the present LCD panel, for the fix of the positioning of the optical films, the adhesive tape 112 sticking on the plastic frame 102 is used and both of them are usually utilized to limit the motion directions of the optical films. The motion in the X-Y direction of the optical films is limited by the plastic frame 102, and the motion in the Z direction of the optical films is limited by the adhesive tape 112.
Referring to FIG. 2, FIG. 2 is a diagram illustrating the utilization of the adhesive tape to fix the optical films. Though the adhesive tape 112 may be utilized to fix the optical films, after a period of time, the decreasing adhesion of adhesive tape 112 may causes the degradation of the positioning of the optical films. FIG. 3A and FIG. 3B illustrate the problems of positioning the optical films by the adhesive tape in the traditional of the position of the optical films. Referring to FIG. 3A, the adhesive tape 112 is not well fixed, such that the optical film 114 is loosed from the recess of the plastic frame 102 and the malposition of the optical films 114 is happened. The dotted line indicates a normal position of the optical film 114 when the optical film 114 does not come off, and the optical film 114 is still fastened within the plastic frame 102. Referring to FIG. 3B, the adhesive tape 112 drops from the plastic frame 102, causing the optical film 114 coming off the plastic frame 102 and displacement. The dotted line 114 indicates a normal position of the optical film 114 when the optical film 114 is fastened within the plastic frame 102. The two situations illustrated in FIGS. 3A and 3B bring defects in the appearance of LCD panel.
Moreover, it is necessary to replace the adhesive tape whenever the product is reworked. It is absolutely a burden to both the fabrication time and the cost of materials.